Recently, from the perspective of environmental protection, a wind power generating apparatus using wind power and other power generating apparatuses using renewable energy such as tidal current, ocean current and river current are becoming popular. In the power generating apparatus of renewable energy type, motion energy of wind, tidal current, ocean current or river current is converted to rotation energy of the rotor and the rotation energy is converted to electric power by a generator.
In such power generating apparatus of renewable energy type, the rotation speed of the rotor is low compared to a rated rotation speed of the generator and thus, a mechanical gearbox is provided between the rotor and the generator. Specifically, the rotation speed of the rotor is increased to the rated speed of the generator by the gearbox and then inputted to the generator.
To improve power generation, efficiency, the power generating apparatus of renewable energy type becomes larger and the gearbox becomes heavier and more expensive as well. In view of this, a power generating apparatus of renewable energy type which uses hydraulic transmission having a hydraulic pump and a hydraulic motor instead of the mechanical gearbox, receives increased attention.
For instance, disclosed in Patent Literatures 1 and 2 is a wind power generating apparatus equipped with a hydraulic transmission formed by a hydraulic installed around a main shaft and a hydraulic motor driven by pressurized oil of the hydraulic pump. In such wind power generating apparatus, the hydraulic pump is driven by the rotation of the main shaft and the hydraulic motor is driven by the pressurized oil supplied from the hydraulic pump so as to drive the generator by the rotation of the hydraulic motor.